Ignoring Self-Signed Certificates from Powershell Invoke-RestMethod doesn't work (it's changed again...)

Question

After using standard solutions for ignoring certificate verification, Invoke-RestMethod is returning:

Invoke-RestMethod : A system error occurred and has been logged.  Please try again later or contact your administrator.

I just noticed this failure today, so I think it has something to do with a Powershell update. By "standard solutions" I mean:

[System.Net.ServicePointManager]::ServerCertificateValidationCallback = { $true }

which stopped working a few months ago, and setting the callback properly in a C# type added to Powershell (description below in History).

Here is my environment:

> $PSVersionTable

Name                           Value
----                           -----
PSVersion                      5.1.15063.674
PSEdition                      Desktop
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0...}
BuildVersion                   10.0.15063.674
CLRVersion                     4.0.30319.42000
WSManStackVersion              3.0
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1

Here is a little history so this question doesn't just get closed as a duplicate.

History

If you Google around or search StackOverflow you can find this question coming up with a few canned responses. However, today I noticed that all of the standard solutions aren't working anymore.

The standard error Powershell gives is:

Invoke-RestMethod : The underlying connection was closed: Could not establish trust relationship for the SSL/TLS secure channel.

The standard answer given on forums everywhere is to use this command before you call Invoke-RestMethod:

[System.Net.ServicePointManager]::ServerCertificateValidationCallback = { $true }

But if you're using an up to date version of Windows 10 / 2016 and Powershell, then your call to Invoke-RestMethod will return:

Invoke-RestMethod : The underlying connection was closed: An unexpected error occurred on a send.

The explanation for why that happens is found on Huddled Masses blog. It can be summarized as:

Setting the ServerCertificateValidationCallback to a scriptblock won't work for an asynchronous callback (one that happens on a task thread), because the other thread won't have a runspace to execute the script on.

Originally, I had been solving that problem with this code:

if (-not ([System.Management.Automation.PSTypeName]"TrustAllCertsPolicy").Type)
{
    Add-Type -TypeDefinition  @"
using System.Net;
using System.Security.Cryptography.X509Certificates;
public class TrustAllCertsPolicy : ICertificatePolicy {
    public bool CheckValidationResult(
        ServicePoint srvPoint, X509Certificate certificate,
        WebRequest request, int certificateProblem)
    {
        return true;
    }
}
"@
}

if ([System.Net.ServicePointManager]::CertificatePolicy.ToString() -ne "TrustAllCertsPolicy")
{
    [System.Net.ServicePointManager]::CertificatePolicy = New-Object TrustAllCertsPolicy
}

But, that didn't work on Windows Server 2016, even though it was working fine on Windows 10. So, based on Huddled Masses I wrote this up to handle certificate validation callbacks in C# rather than a script block:

function Disable-SslVerification
{
    if (-not ([System.Management.Automation.PSTypeName]"TrustEverything").Type)
    {
        Add-Type -TypeDefinition  @"
using System.Net.Security;
using System.Security.Cryptography.X509Certificates;
public static class TrustEverything
{
    private static bool ValidationCallback(object sender, X509Certificate certificate, X509Chain chain,
        SslPolicyErrors sslPolicyErrors) { return true; }
    public static void SetCallback() { System.Net.ServicePointManager.ServerCertificateValidationCallback = ValidationCallback; }
    public static void UnsetCallback() { System.Net.ServicePointManager.ServerCertificateValidationCallback = null; }
}
"@
    }
    [TrustEverything]::SetCallback()
}
function Enable-SslVerification
{
    if (([System.Management.Automation.PSTypeName]"TrustEverything").Type)
    {
        [TrustEverything]::UnsetCallback()
    }
}

That worked really well for a long time, but just recently I started getting the following error back when I call Invoke-RestMethod:

Invoke-RestMethod : A system error occurred and has been logged.  Please try again later or contact your administrator.

I understand that a proper solution is just to deploy certificates, but often you just want to test things out without having to set up a proper PKIX.

Solution

I think I have narrowed this down to a change in the web service that I'm calling. Doh!

The Disable-SslVerification and Enable-SslVerification function that I listed in my question are still the best way to go and seem to work.

I look forward to the -SkipCertificateCheck switch mentioned by Bacon Bits in the comments. Then, we can stop hacking. =)

Hopefully this question is valuable for people who are trying to solve the same problem but run into the An unexpected error occurred on a send problem.